In #33325, `deprecate_methods` is replaced from `prepend` to completely
emurated `alias_method_chain`, it exposed two internal methods
`xxx_with_deprecation` and `xxx_without_deprecation`.
After that, #34648 restored the `prepend` implementation, which doesn't
expose any internal methods, so we no longer be able to ensure to always
expose that internal methods.
As I said at https://github.com/rails/rails/pull/33325#issuecomment-409016725,
I think that internal methods exposed is not a specification but a
limitation when using `alias_method_chain`, there is no longer a reason
to follow that limitation.
- Refactoring alias_chain to Module#prepend broke the possibility to deprecate class methods since the module
generated was prepended to the target's instance.
A suggestion to fix this was to use `AS#redefine_method` which would solve the
problem but with the cost of redefining directly the method.
Decided to go with the same alias_chain implementation as before instead.
- Fixes#33253
This commit fixes `deprecate` so that it preserves method visibility (like it
did previously when it was utilizing `alias_method_chain`).
When Module#prepend replaced alias_method_chain in a982a42 it caused deprecated
methods to always become public.
`alias_method_chain` had this bit of code:
https://github.com/rails/rails/blob/v5.0.6/activesupport/lib/active_support/core_ext/module/aliasing.rb#L40-L47
which preserved method visibility.
Without this fix, a workaround would be:
```ruby
class C8
private
def new_method
end
def old_method
end
deprecate :old_method, :new_method
# workaround:
instance_method(:old_method).owner.send(:private, :old_method)
end
```
Because the visibility needs to be fixed on the Module prepended by
MethodWrapper.
Add tests for ActiveSupport::Deprecation.deprecate_methods
Modify ActiveSupport::Testing::Deprecation to allow a custom deprecator
Leverage ActiveSupport::Testing::Deprecation assert_deprecated
Update documentation for ActiveSupport::Deprecation.deprecate_methods
Use cases:
Using the default deprecator => "removed from Rails X.Y"
Passing a custom deprecator in the options hash => "removed from MyGem next-release"
Deprecating methods directly from custom deprecator => "removed from MyGem next-release"
